1. Field of Invention
The present invention generally relates to satellite position location systems and, more particularly, to a method and apparatus for processing position information in a mobile device.
2. Description of the Background Art
In an effort to enhance GPS signal processing, a GPS receiver (also referred to as a mobile station or MS) can be assisted with certain a-priori information. Such assisted GPS (A-GPS) receivers generally are provided with an estimate of the receiver's position and information regarding the satellite constellation (e.g., ephemeris, satellite orbit information and/or a satellite almanac). The information is provided to the A-GPS receiver via a wireless network such as, for example, a cellular telephone network. In an MS-based mode, an A-GPS receiver uses the assistance information and the received GPS signals to compute its position. This position is then sent to a position server for use by the network (e.g., to be forwarded to an emergency response provider such that the provider receives the location of the cell phone user).
Generally, the position server requests that the position be computed by the MS in a predefined period. The MS processes the GPS signals in an iterative process such that, from an initial, inaccurate position estimate, an accurate position is determined as GPS signals are repeatedly received and processed. In a low signal level environment (e.g., indoors), the MS may require an extensive period of time to compute an accurate position. At times, the computation period required to determine an accurate position may be longer than the predefined period. When that happens, the MS stops computing at the end of the predefined period and sends the server the last computed position, whether accurate or not. Such an inaccurate position can be problematic when the position is being used to locate a user to provide emergency services.
In other versions of an A-GPS receiver, the receiver may have an internal timer that establishes a time period within which the position is calculated. The receiver produces the last position computation result as the “correct” position. However, the last result may not be the most accurate result. As such, an inaccurate result may be sent to the server or displayed to the user.
Therefore, there is a need in the art for an improved method, apparatus, and system for determining a position of an A-GPS receiver.